首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22092篇
  免费   183篇
  国内免费   167篇
安全科学   611篇
废物处理   896篇
环保管理   2944篇
综合类   4334篇
基础理论   5409篇
环境理论   12篇
污染及防治   5624篇
评价与监测   1343篇
社会与环境   1135篇
灾害及防治   134篇
  2022年   189篇
  2021年   185篇
  2020年   131篇
  2019年   159篇
  2018年   298篇
  2017年   266篇
  2016年   429篇
  2015年   343篇
  2014年   493篇
  2013年   1631篇
  2012年   618篇
  2011年   883篇
  2010年   709篇
  2009年   822篇
  2008年   908篇
  2007年   955篇
  2006年   851篇
  2005年   735篇
  2004年   682篇
  2003年   703篇
  2002年   643篇
  2001年   845篇
  2000年   617篇
  1999年   389篇
  1998年   232篇
  1997年   264篇
  1996年   259篇
  1995年   324篇
  1994年   320篇
  1993年   269篇
  1992年   246篇
  1991年   305篇
  1990年   274篇
  1989年   270篇
  1988年   235篇
  1987年   221篇
  1986年   192篇
  1985年   181篇
  1984年   223篇
  1983年   224篇
  1982年   229篇
  1981年   199篇
  1980年   178篇
  1979年   205篇
  1978年   157篇
  1977年   151篇
  1976年   134篇
  1975年   156篇
  1974年   156篇
  1973年   130篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
361.
362.
363.
The sinusoidal fetal heart rate pattern has been described in association with severe fetal anaemia, with fetal hypoxaemia, and with the administration of parenteral narcotics. Here, we report a case of decreased fetal movement in which a sinusoidal tracing was recorded. The sonographic diagnosis of a massive fetal intracranial haemorrhage was made. A non-interventive approach was taken and the fetus died soon after in utero. We review 28 previous cases in which the prenatal sonographic diagnosis of fetal intracranial haemorrhage was made, including the underlying maternal and fetal factors and neonatal outcomes. We propose that the sinusoidal tracing in this case was due to the intracranial bleed and suggest that fetal intracranial haemorrhage be considered in the sonographic evaluation of the fetus with a sinusoidal pattern.  相似文献   
364.
We report two cases of apparently balanced complex de novo chromosomal rearrangements (BCCR) detected prenatally at 17 weeks and 10 weeks of gestation, respectively. Chromosomes were studied using GTG-banding and fluorescent in situ hybridization (FISH). In one case four chromosomes and in the other case three chromosomes were involved in the rearrangements. One of the pregnancies was terminated and no external or internal abnormalities were detected at autopsy. The other pregnancy continued to term. Level III ultrasound examination showed no abnormalities. The child is now 3 years old and has neither congenital anomalies nor evidence of delayed psychomotor development.  相似文献   
365.
366.
367.
IntroductionFertilizationisessentialforagriculturalproduction ,butunreasonablyapplyingfertilizerscouldresultinseriesofproblemssuchascropqualitydecline,fertilizeruseefficiencydecrease,residualfertilizerspollution groundwaterandriversandnitrogencontented …  相似文献   
368.
The coastal seawater of Mediterranean of Alexandria receives large amount of discharged waters containing industrial wastes, sewage, and agricultural and domestic drainage. Fluoride and some parameters were(chemical and physical) determined. The data gave indication that the content and the amount of the discharged water largely affect the chemical composition of the coastal water. Stepwise regression analysis was highly significant and the model was very fruitful, where the observed and calculated values were mostly concordant. This may indicated that there was a relation between fluoride content in coastal seawater and its content in the discharged water.  相似文献   
369.
Variability in the level of expression of very long chain fatty acids (VLCFAs) is documented in cultured chorionic villus (CV) cells derived from two fetuses, one at risk for an unusual peroxisomal fatty acid β-oxidation defect, and the other at risk for the X-linked form of adrenoleucodystrophy (ALD). Cells from early subcultures of chorionic cells from both cases gave normal values for VLCFA ratios. The results for the fetus at risk for the β-oxidation defect were interpreted to indicate that the fetus was not affected; however, at birth, the infant was clinically and biochemically affected. In the case of the fetus at risk for X-linked ALD, although VLCFAs were normal in subculture 1, the levels of these fatty acids increased dramatically in subculture 3, suggesting an abnormal fetus. Termination of the pregnancy and subsequent biochemical and morphological follow-up confirmed that the fetus was indeed affected by ALD.  相似文献   
370.
Ten-ml samples of amniotic fluid were taken from pregnancies being terminated at 8–14 weeks' gestation. DNA was extracted from the amniotic cells by sequential centrifugation and analysed using the polymerase chain reaction (PCR). Fifteen samples were analysed for evidence of maternal contamination using Mfd5 oligo-nucleotide primers for repeat polymorphisms. Ten amniotic fluid samples were tested for the Delta-F508 deletion characteristic of cystic fibrosis to demonstrate a diagnostic application for the technique. In each case, DNA extracted from fetal tissue from the same pregnancy was included in the controls. In 14 of the 15 cases tested with the Mfd5 primers, both the amniotic fluid DNA and the fetal DNA showed no evidence of contaminating DNA. In one case, neither the amniotic fluid cells nor the fetal cells yielded results. In nine of the ten cases tested with the Delta-F508 primers, the amniotic fluid cell DNA provided accurate information about the genetic status of the fetus; in the tenth, the fetal DNA failed to amplify. The results indicate that adequate DNA can be extracted from amniotic fluid from 8 weeks' gestation onward and these samples are suitable for prenatal diagnosis using PCR.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号